In recent years, electronic devices exploiting organic semiconductor materials have been developed widely, and many reports have been made on the development of an organic electro-luminescence (EL) and an organic thin film transistor (TFT), an organic semiconductor laser, and the like.
Of those, the organic TFT, a kind of organic transistors, does not require a high temperature process during its fabrication, and therefore is promising as a technique with which integrated circuits can be constructed on an inexpensive substrate made of glass, resin, or the like at a low cost by employing a printing technique or the like.
Meanwhile, a semiconductor integrated circuit of a nonvolatile memory, which retains information even after its electric power source is turned off, has been generally composed of a system formed by using single crystalline silicon. However, in recent years, elements and circuits exploiting noncrystalline silicon such as amorphous silicon or polycrystalline silicon or utilizing a non-silicon-based semiconductor such as an organic semiconductor or a diamond or silicon carbide semiconductor are rapidly developed.
For example, U.S. Pat. No. 6,034,882 discloses a configuration in which an impedance is varied by applying to the storage element a write voltage inducing the breakdown of a dielectric contained in a storage element, whereby a memory effect is attained.
If such a memory device is fabricated by using the above-mentioned organic semiconductor element, the fabrication is expected to be at a low cost. However, memory configurations having functions comparative with those of a flash memory and an electrical erasable programmable read only memory (EEPROM) made of single-crystalline silicon are not disclosed in the present circumstances.
Further, for example, there is proposed a configuration using a phenomenon in which a current exhibits a binary state at a certain read voltage due to a threshold voltage shift of an organic transistor as described in Journal of American Chemical Society, 2003, vol. 125, pp. 9414-9423. However, an applied voltage and its time period necessary for inducing a sufficient threshold voltage shift for achieving this binary state are 100 V and 1 minute, respectively, and this is difficult in practical use.
Moreover, Japanese Patent Application Laid-Open No. 2001-189431 discloses a configuration capable of carrying out multi-valued storage by using an organic material for a storage element and fluctuating an impedance of the element with a voltage.